Maturation of primary transcription products entails cleavage reactions (both endonucleolytic and nucleotide) modification. A detailed molecular understanding of these reactions should thus elucidate 1) specific criteria which govern protein-nucleic interactions, and 2) the biological significance of RNA processing. Upon infection of E. coli, the bacteriophage T4 codes for the synthesis of 8 new tRNA species. Six of these RNA's have been identified on three different precursors, each of which is dimeric -- i.e., contains the sequences of two tRNAs. Each contains 10-15 extra nucleotides located at the 5' and 3' termini; these sequences are all A-U rich, but each is unique. The most striking disparity is the presence (and location) or absence of the universal 3' terminal sequence -CCAOH. The requirement for post-transcriptional addition of this sequence is probably a rate-limiting step in the maturation of these tRNAs. Conformation rather than primary sequence is the crucial criterion for efficient and accurate processing. Thus, another goal will be the elucidation of these structural features using a unique biochemical approach together with mutant analysis. Both the qualtity and quantity of mature product is regulated at the level of RNA processing, and primary focused on 3' maturation.